Trends and interventions in large whale entanglement along the South African coast

The major causes of large whale entanglement in South Africa are static fishing gear, especially the type associated with the West Coast rock lobster Jasus lalandii industry, and large-mesh gillnets that are set off the coast of KwaZulu-Natal (KZN) to reduce shark attacks (shark nets). The prevalence of entanglements is seasonal with the peaks in activity coinciding with the breeding migrations of humpback whales Megaptera novaeangliae and southern right whales Eubalaena australis, the two large whale species that are the most prone to entanglement. Generalised linear models with a Poisson or quasi-Poisson distribution were used to describe the relationship between the number of incidents and time. Taking into account the combined length of shark-net installations per year as an offset variable, entanglement of humpback whales in shark nets increased at 15.1% per year (95% CI = 9.5–21.6%) from 1990 to 2009. This is comparable to the rate of increase in the numbers of this species migrating past the KZN coast, between 1988 and 2002 (9–11%). The number of reported incidents of southern right whales entangled in gear other than shark nets also increased between 1990 and 2009. This was accounted for by the increase in numbers of this species in South Africa (7% per year), so in neither case are the two species at increasing risk of individual entanglement, and anthropogenic factors including entanglement do not seem to be affecting the recovery of these whale populations. Nevertheless, there is concern regarding the vulnerability to entanglement of a small assemblage of humpback whales that habitually visits the West Coast in spring and summer. The continued recovery of whale populations is likely to lead to greater levels of anthropogenic interaction and heighten the need for adequate mitigation measures. The KZN Sharks Board and the South African Whale Disentanglement Network (since 2006) have respectively released (disentangled) 81% and 23% of confirmed entangled individuals, and recorded relevant information on entanglement incidents. Such information is critical for developing mitigation measures and monitoring the prevalence of entanglement.     

Implications of Arctic industrial growth and strategies to mitigate future vessel and fishing gear impacts on bowhead whales

The objective of this paper was to investigate and illustrate how insights gained from experience managing human activities in order to protect North Atlantic right whales (Eubalaena glacialis) along the heavily industrialized east coast of North America might be applied in the Arctic, where bowhead whales (Balaena mysticetus) face some of the same risks as right whales. The reduced extent and thickness of sea ice and the resultant longer open-water season have major, complex implications for the Arctic marine ecosystem. Increased maritime ship traffic and commercial fishing in the Arctic are bound to affect bowheads and Native (indigenous) hunting communities who depend on whales for subsistence and cultural identity. Bowheads and right whales were greatly depleted by commercial whaling in the 19th and early 20th centuries. While the Western Arctic bowhead population has been recovering steadily in recent decades, North Atlantic right whales remain highly endangered because of persistent lethal and sublethal vessel strikes and frequent entanglement in commercial fishing gear. Entanglement can be transitory or persistent, with debilitation lasting for months before the animal finally succumbs. Vessel strike and fishing gear trauma has been documented in bowheads, but at a much lower rate than in right whales. Initiatives intended to mitigate the impacts of ship traffic on North Atlantic right whales have included speed limits and routing changes. Those meant to reduce the incidence and severity of entanglements include the modification of gear design and gear deployment practices. Management measures need to be considered in advance in the Arctic in order to minimize the risks to bowhead whales as shipping and industrial fishing expand in the Arctic with ice retreat.     

Whale interactions with Alaskan sablefish and Pacific halibut fisheries: Surveying fishermen perception,changing fishing practices and mitigation

Whale depredation occurs when whales steal fish, damage fish or damage fishing gear. In Alaska, killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) primarily depredate on demersal sablefish (Anoplopoma fimbria) and Pacific halibut (Hippoglossus stenolepis) longline fisheries. Quantitative data on whale depredation in Alaska is limited due to low fishery observer coverage and minimal depredation evidence left on longline fishing gear. This study utilized semidirected interviews (n=70) and written questionnaires (n=95) with longline fishermen to examine: (1) perceptions and experiences of whale–fishery interactions in Alaska, (2) effects of depredation on fishing practices, and (3) potential depredation mitigation measures. Eighty-seven percent of fishermen surveyed agreed that whale depredation became worse between 1990 and 2010. Respondents reported changing their fishing practices in response to depredating whales in several ways, including: traveling up to 50 nautical miles and ceasing hauling operations up to 24 h until the whales left the fishing grounds. Respondents fishing in western Alaska, primarily encountering killer whales, were forced to wait longer and travel greater distances than fishermen operating in central and southeast Alaska, regions more affected by sperm whales. Deterrent research, gear modifications and real-time tracking of depredating whales were solutions favored by study participants. Survey respondent answers varied based on areas fished, quota owned, years involved in the fishery and vessel size. This study presents the first statewide evaluation of fishermen's perception and knowledge of whale interactions with the Alaskan longline fleet and is a critical step toward developing baseline data and feasible depredation mitigation strategies.     

Geospatial analysis of management areas implemented for protection of the North Atlantic right whale along the northern Atlantic coast of the United States

The North Atlantic right whale (Eubalaena glacialis) is a critically endangered large whale species found in waters off the U.S. and Canadian Atlantic coasts. The primary human-caused threats are entanglement in fishing gear and collisions with vessels. Since 2002, NOAA's National Marine Fisheries Service has implemented both seasonally and dynamically managed protective zones where right whales occur to reduce these threats; Seasonal Area Management (SAM) and Dynamic Area Management (DAM) for the reduction of right whale entanglements with fishing gear, and Seasonal Management Areas (SMA) and Dynamic Management Areas (DMA) for reduction of vessel collisions. This paper analyzes the presence of frequent concentrations of right whales outside of SAM and SMA zones, represented by the spatial and temporal occurrence of DAMs and DMAs. A grid of 1 min×1 min squares was geospatially applied to locations of DAMs and DMAs from April 2002 through June 2011 and the number of management areas that intersected each 1 min square was populated. DAMs and DMAs were most highly concentrated along the central Gulf of Maine. Of the 131 DAMs and DMAs implemented, 97 (74.0%) intersected this area, and were primarily implemented from October through February. The results of this analysis will aid in consideration of possible modifications to the size and location of SMAs along the northern Atlantic coast of the U.S. and other management actions for the reduction of vessel collisions with right whales.     

Managing U.S. Atlantic large whale entanglements: Four guiding principles

Fatal entanglements in fishing gear threaten marine mammal populations worldwide. The management of entanglements of large whales, such as the North Atlantic right whale (Eubalaena glacialis), with commercial fisheries, is a challenge given the species’ small population size, economic consequences of regulations, and the general lack of data on entanglements. The U.S. Marine Mammal Protection Act (MMPA) requires development of programs to limit marine mammal entanglement in commercial fishing gear. Following a retrospective look at implementing aspects of the MMPA, a set of guiding principles were developed with associated best practices useful in reducing fatal large whale entanglement in fishing gear. Among these are: 1) involve stakeholders early in the decision making process; 2) establish a transparent management strategy that includes critical needs to guide research; 3) use a variety of tools such as an established process for receiving new information and ideas; and 4) incorporate adaptive management which considers the constraints of dynamic (rapid) changes to some fixed fishing gear. Efforts to reduce worldwide marine mammal bycatch will typically occur in a data-limited environment as experienced with U.S. Atlantic large whale entanglements. The guiding principles will remain as key tools for reducing large whale bycatch in fisheries as they build upon common practices. These insights developed over two decades of management can potentially help others to address similar bycatch problems.     

Spatial and temporal assessment of potential risk to cetaceans from static fishing gears

Ecosystem Based Fisheries Management (EBFM) requires the consideration of potential impacts of a commercial fishery on all components of the ecosystem. Assessment of the impact of commercial fishing on marine mammals generally focuses on species at known risk from bycatch. For cetaceans in particular, inclusion under the Threatened, Endangered and Protected (TEP) species component of Ecological Risk Assessment for the Effects of Fishing (ERAEF) can seem redundant if a species is already known to be at risk or is not thought to interact with the fishery with consequences for its conservation. A spatially and temporally explicit Productivity Susceptibility Analysis (PSA) procedure was developed for inclusion under ERAEF to allow cetacean species to be screened for risk. The technique is demonstrated by assessing the potential risk to harbour porpoise and minke whales from a number of static gear fisheries. The results demonstrate that although a fishery might pose high risk to a species, low or moderate risk areas can exist within the range of the fishery, enabling management measures to focus on areas of greatest risk. Designed to complement and support existing methods of bycatch assessment, this approach is a repeatable and standardised assessment, the outputs of which can be used to systematically document the level of risk posed to different species in a transparent way to aid the inclusion of cetaceans in ERAEF and EBFM both now and in the future.     

Seals and fisheries in South Africa — competition and conflict

There are two types of interactions between seals and commercial fisheries in South Africa: biological (potential competition for shared resources between the two "predators") and operational (conflicts during fishing operations). Using data for the 1980s, a comparison is made of relative consumption by different predators in South African waters. Seals and fisheries are not the major consumers in the system, but they do take comparable amounts. This has resulted in calls for a reduction in the seal population, but to date, no studies have shown that reducing seal predation of commercial species will make more fish available for the fisheries. Most fisheries are subject to some form of operational interaction with seals. These interactions include consumption of catches (operational consumption), disturbance of fishing operations (operational disturbance) and damage to fishing gear (operational gear damage); they vary in degree of severity, both seasonally and regionally. Estimates of the consumption by seals from fishing operations in South Africa show it to be a minimal percentage of fishery catches and a small proportion of the total predation by seals. Preliminary calculations of overall economic losses resulting from seal interference show this to be small in comparison with the wholesale value of the catches. Seals die as a result of fishing operations, and estimates of the potential mortality through entanglement, drowning and deliberate killing indicate this mortality to be of a magnitude that should be monitored.     

基于BiLSTM模型的远洋渔船类型识别研究

船舶自动识别系统(Automatic identification system,AIS)为渔业资源和渔船捕捞活动管理和研究提供了可能.明确船舶作业类型是开展AIS信息渔业研究应用前提,为渔业研究和管理提供渔船捕捞类型基础数据支撑,保障渔船作业安全和监督非法捕捞渔业活动,作者通过搜集整理3000多艘已知类型船舶信息,从...     

Ecological risk assessment of the Marshall Islands longline tuna fishery

To support implementing an ecosystem approach to fisheries management, ecological risk assessment (ERA) methods have recently been developed for the continuum of data-deficient to data-rich fisheries. A semi-quantitative ERA was conducted for the Marshall Islands longline bigeye tuna (Thunnus obesus) fishery. The study used information from analyses of observer data, surveys of captains and crew and inventories of gear and equipment. Relative risks were evaluated through a consideration of phylogenetic uniqueness, risk of population extirpation, risk of species extinction and importance in ecosystem regulation. The fishery presents a highest relative risk to leatherback (Dermochelys coriacea), hawksbill (Eretmochelys imbricata), green (Chelonia mydas) and olive Ridley (Lepidochelys olivacea) sea turtle Regional Management Units that overlap with the fishery, in that order. The next highest relative risk is to affected stocks of oceanic whitetip (Carcharhinus longimanus), blue (Prionace glauca), and silky (Carcharhinus falciformis) sharks, in that sequence. Seabird bycatch is likely not problematic. There was inadequate information to assess risks to cetacean populations. Risks to stocks of market and non-market species of marine fishes with r-selected life history characteristics were not assessed. This is because estimates of critical threshold levels of local and absolute abundance and current biomass are not known for many of these stocks. Several best practice gear technology methods to mitigate problematic catch of vulnerable species groups are currently employed: monofilament leaders, whole fish for bait, single-hooking fish bait, no lightsticks, and no fishing at shallow submerged features. Setting terminal tackle below 100 m and carrying and using best practice handling and release equipment were methods identified to reduce fishing mortality and injury of vulnerable species. More information is needed to determine if weaker hooks should be prescribed to mitigate cetacean bycatch. The large benefit to sea turtles of replacing remaining J-shaped hooks with circle hooks might outweigh a possible small increase in elasmobranch catch rates. The consumption of 2024 l of fuel per tonne of landed catch, which is within the range of available estimated rates from similar fisheries, could be reduced, reducing greenhouse gas emissions, through more frequent maintenance and upgrading vessel equipment and materials. Observer data quality may be adequate to support a quantitative Level 3 ERA to determine the significance of the effect of various factors on standardized catch rates and to estimate population-level effects from fishing mortality.     

Investigation into the declining trend in chokka squid Loligo vulgaris reynaudii Catches made by South African trawlers

The trawl fishery, which targets Cape hake Merluccius spp. and Agulhas sole Austroglossus pectoralis, takes chokka squid Loligo vulgaris reynaudii as by-catch. Catch and effort data from the trawl fishery for the period 1978–1996 are used to obtain annual estimates of catch rate (catch per unit effort cpue) for that period. Examination of the cpue trend shows a sharp decline in the early 1980s and, in order to identify factors that could have influenced that decline, the distribution of fishing effort is investigated both temporally and spatially. There is a possible change in the incidence of squid-directed catches over time, but their overall scarcity could have had only a small impact on the annual cpue trend. Further, using distribution of fishing effort to evaluate the effects of possible changes in fishing patterns, rather than changes in resource abundance, on the trend in trawl cpue, it became clear that there had been a contraction of the trawling grounds and changes in fishing patterns in relation to depth over time. Finally, a general linear model (GLM) is developed to quantify the effect on cpue of factors such as vessel characteristic, depth and position of the drag, season and target species, so obtaining a standardized trawl cpue index of chokka abundance. Analysis of that trend reveals a mean 7.7% annual decline for the period investigated, which should be interpreted as a strong sign of resource decline.     

Analysis of bycatch in the South African midwater trawl fishery for horse mackerel Trachurus capensis based on observer data

The South African midwater trawl fishery targets adult horse mackerel Trachurus capensis. The bulk of the catch is taken by a single freezer-trawler, the biggest fishing vessel operating in South African waters. As fishing takes place off the south coast in ecologically sensitive areas, there are concerns about the potential impacts of this fishing operation on non-target species. Fishing behaviour and bycatch of this fishery from 2004 to 2014 were investigated by analysing observer records with regard to catch composition, volume and temporal and spatial patterns. The midwater trawl fishery was estimated to have caught 25 415 tonnes annually, with a bycatch of 6.9% of the total catch, by weight. There are species overlaps with various fisheries, namely the demersal trawl, small-pelagic, line, shark longline and squid fisheries, yet the total bycatch estimates from this fishery are generally small relative to catches taken in the target fisheries. Bycatch species with the highest average annual catches were chub mackerel Scomber japonicus, redeye roundherring Etrumeus whiteheadi, ribbonfish Lepidopus caudatus and hake Merluccius spp. Large-fauna bycatch species included sunfish Mola mola as well as a number of CITES II- and IUCN-listed species, such as Cape fur seal Arctocephalus pusillus, dusky shark Carcharhinus obscurus, smooth hammerhead shark Sphyrna zygaena and thresher sharks Alopias spp. The 97.9% observer coverage is high and the 6.9% bycatch rate low compared to other South African fisheries; however, due to the large size of the individual hauls (average of 46.3 t), the average sampling rate of 1.56% is low. Our analyses suggest that bycatch in the South African midwater trawl fishery has been lower than in other South African fisheries and similar fisheries elsewhere, but due to the combination of high catch volumes and low sampling rates, estimation errors for rare species are high and there is a substantial risk of incidental unmonitored bycatch of rare large fauna and aggregations of small fauna. This could be mitigated by spatio-temporal management of this fishery, to avoid fishing in high-risk areas, and the introduction of an electronic monitoring programme.     

Using fine‐scale catch predictions to examine spatial variation in growth and catchability of Panulirus cygnus along the west coast of Australia

Puerulus settlement has been monitored throughout the western rock lobster Panulirus cygnus fishery for nearly 40 years. These data, in combination with indices of effort and water temperature, were used to produce recruitment‐catch relationships for each 1° transect of latitude in the coastal part of this fishery from Kalbarri to Cape Leeuwin, as well as at the offshore Abrolhos Islands (total of eight transects). The fine spatial scales of these models provided estimates of certain life history traits that are known to affect lobster catches between adjacent fishing ports. This catch modelling showed that the proportions of 3‐ and 4‐year‐old post‐settlement lobsters contributing to the catches varied markedly from the southern to northern transects, suggesting that juvenile lobsters grow substantially faster in the warmer northern and offshore waters of this fishery. These proportions provide accurate estimates of juvenile growth rates, which are vital in the construction of location‐specific growth algorithms required by the age‐structured models used in the management of this fishery. Model estimates of density‐dependent mortality were greater in the more densely populated centre of the fishery and markedly lower at the northern and southern limits of this species distribution. Annual increases in fishing efficiency were also found to be lowest at the northern and southern extremes of the fishery and greatest in the centre of the fishery, where technology advances and increased fleet mobility have enabled the fleet to increase efficiency by 1–3% each year. Catchability (q) was found to be most influenced by water temperatures in the cooler southern transects, whereas at the Abrolhos Islands, changes in water temperature produced almost no discernable change in q. The catch modelling was also used to quantify the impact of management changes introduced in the 1993/94 fishing season. Increased protection of female lobsters and an 18% pot reduction resulted in a 3–4% permanent reduction in the catch rates of lobsters throughout most of the coastal fishery, whereas at the offshore Abrolhos Islands, catch rates increased by c. 20%, presumably owing to a reduction in the level of pot saturation.     

Assessment of the exploitable biomass of thread herring(Opisthonema spp.) in northwestern Mexico

In recent years, the small pelagic fishery on the Pacific northwest coast of Mexico has significantly increased fishing pressure on thread herring Opisthonema spp. This fishery is regulated using a precautionary approach(acceptable biological catch(ABC) and minimum catch size). However, due to fishing dynamics, fish aggregation habits and increased fishing mortality, periodic biomass assessments are necessary to estimate ABC and assess the resource status. The Catch-MSY approach was used to analyze historical series of thread herring catches off the western Baja California Sur(BCS, 1981–2018) and the Gulf of California(GC, 1972–2018) to estimate exploitable biomass and target reference points in order to obtain catch quotas. According to the results, in GC,the maximum biomass reached in 1972(at the beginning of fishery) and minimum biomass reached in 2015; the estimated exploitable biomass for 2019 was 42.2×10~4 t; and the maximum sustainable yield(MSY) was 15.4×10~4 t.In the western BCS coast, the maximum biomass was reached in 1981(at the beginning of fishery) and minimum biomass was reached in 2017; the estimated exploitable biomass for 2019 was 3.2×10~4 t; and the MSY was 1.2×10~4 t.Both stocks showed a decrease in biomass over the past years and were currently near to point of full exploitation.The results suggest that the use of the Catch-MSY method is suitable to obtain annual biomass estimates, in order to establish an ABC, to know the current state of the resource, and to avoid overcoming the potential recovery of the stocks.     

The introduction of limited entry: The New Zealand rock lobster fishery

The author describes the implementation of a controlled or limited entry fishery for New Zealand rock lobsters. The background to the implementation of limited entry is described and the decrease in annual landings per vessel in the period 1955–1977 is pointed out. The New Zealand licensing system is outlined, attention being paid to continuous and seasonal licences, allocation of licences, controlled fishing areas, and fishing methods and gear restrictions. The number of rock lobster vessels decreased from 1574 in 1979 to 970 after the initial round of licensing.     

论渔业法之使用小于最小网目尺寸的网具进行捕捞行为的法律责任

渔业资源的可持续发展是实现渔业捕捞可持续发展的基石,明确使用最小网目尺寸的网具进行捕捞,有利于幼鱼从网具中释放,最终达到渔业捞捕可持续发展的目的。为保障渔业捕捞可持续发展,文章分析使用最小网目尺寸的网具进行捕捞行为的处罚裁量基准、网目尺寸制度、没收渔具和执法程序中存在的问题,提出加强源头治理、细化罚款幅度、加快发布《全国海洋捕捞渔具目录》、同一水域协同管理、完善没收渔具定义以及建立渔政联合执法机制等建议。     

An empirical analysis of the economic value of ocean space associated with commercial fishing

Understanding the economic value of ocean space is critical for implementing marine spatial planning (MSP). Empirical data from 1999 to 2008 are compiled on the economic values arising from commercial fishing in the Gulf of Maine and adjacent areas. The data are analyzed to characterize factors affecting the spatial and temporal distribution of measures of economic productivity and fishing effort. The analysis consisted of four components: (1) estimation of net revenue at the 10-min square level by season and gear; (2) assessment of variability for catch revenue and catch per unit effort; (3) mapping net revenue and variability in the study area; and (4) estimation of interactions among catch, effort, season, and gear type. The results indicated that, at each location, average fishing efforts exhibited a positive response to increases in expected revenues and a negative response to variability in revenues. Most of the variability in catch revenue can be explained by changes in fishing effort, implying that the spatial patterns of fishery resources are relatively stable at the 10-min square level. An important conclusion is that a spatial scale of at least the 10-min square is appropriate for undertaking MSP involving allocations of commercial fisheries.     

Fishers' perception of a multiple-use marine protected area: Why communities and gear users differ at Mafia Island,Tanzania

This study examined the perceptions of fishers from two fishing communities with differing use histories and involvement in the long-standing (16 yr) multiple use Mafia Island marine protected area (MIMP), Tanzania. A randomly distributed questionnaire indicated that 94% of fishers believed that without the MIMP, there would be overfishing, dynamite use, destroyed habitats, and few fish. Fishers were more positive about core zones (no-take fishery closures) than general use zones (areas allowing selective fishing) as a consequence of increases in fishing pressure. Those that reported increased catches and sizes of fish since the creation of the MIMP were more likely to agree with present zone locations and more positive in general about fisheries and conservation planning. Most thought that fish size and gear restrictions were preferable to permanent closures. Perceptions differed among communities and gear users. Community and gear type explained 46% of the variance in responses about the perception that fisheries and conservation are compatible goals. Somewhat surprisingly, these effects were more important than catch increases or involvement in MIMP-related activities. The differences in perception between communities may be partly attributed to different fishing histories. Multiple-use zoning provides a means to identify and resolve conflicts and achieve what are likely universal objectives for fisheries sustainability and conservation.     

Management of the precious coral fishery in Taiwan: Progress and perspectives

Precious corals have been commercially exploited because of their legendary and cultural importance for many centuries in the Mediterranean and for almost one century in the Northwest Pacific. Although the precious coral fishery in Taiwan dates back to the 1920s, relevant studies on biology and ecology of resources are relatively scarce. The management of the precious coral fishery in Taiwan was officially instituted in January 2009, when data on the catch and effort of the fishery were recorded. In this study, the catch-effort data of the fishery were examined to explore the temporal and spatial patterns in composition and abundance of Corallium and Paracorallium spp. around Taiwan. A total landing of 3233.0 and 2906.8 kg precious corals were recorded for 2009 and 2010, respectively. Less than 5% of those amounts were from live colonies. A high proportion of fossilized colonies in the catch reflect the non-selective nature of the fishing gear; however, the factors that cause colonies to collapse are not exclusive to the impact of the fishery. Momo coral was dominant in the production for both years, followed by Miss coral. The total production of precious corals correlated positively with fishing efforts, while a weak relationship was found between the production of live colonies and fishing efforts. The fishing efforts mainly aggregated in designated fishing ground A (DFG-A) for both years, while the production of live colonies mainly occurred in DFG-E. The monthly occurrence rate of live colonies decreased over the past 2 years. Although fluctuating significantly, the CPUE of dominant species exhibited an apparent decreasing pattern. High aggregation of the fishing efforts in specific regions and low numbers of live colonies in the production should be carefully taken into account when amending management regulations in the future. The establishment of marine protected areas, in addition to the strict controls that already apply, should be considered to not only sustain the population structure of the sessile animals but also their function in the marine ecosystem.     

Estimating present and future profits within the Namibian hake industry: a bio-economic analysis

Namibia's fishing industry is managed using a system of fishing rights and individual fishing quotas. This property rights system was intended to encourage the local fishing industry to exploit the resource responsibly. Unfortunately, unintended perverse incentives have promoted induced overcapacity and inefficient use of vessels. In combination with inconsistent quota allocations, the result has been persistent pressure on the already depleted biological resource. This paper uses a bio-economic model to estimate actual and potential profits in Namibia's hake fishery. N$300 million annual profit was not realised due to the depressed state of the resource. Mean annual profits for the years 2007–2009 were N$80 million, which provides the fishing industry, as a whole, only about 36% of the potential normal profit. Theoretically this implies that the fishing industry would probably receive better returns with less risk if they invested their money elsewhere. This study demonstrates that by rationalising quotas and improving management, better efficiency and higher profits for the fishers and government could be obtained.     

Fishery management techniques: Practical aspects and limitations

This article investigates practical aspects and limitations of various fishery management techniques. Restrictions on catch and fishing effort (active regulations) are described, and the authors point out that catch restrictions are less robust scientifically than effort restrictions. Spatial — temporal restrictions, gear restrictions, and restrictions on the nature of the catch-which are passive with respect to fishing mortality-are reviewed and it is concluded that fishing mortality is theoretically unbounded when only passive methods of fisheries management are applied.